Project Summary Rheumatoid arthritis (RA) affects up to 2% of the general population in North America. While several effective treatments have been developed, the cause of RA is still not fully understood and there is still no cure. In addition, the treatment of RA is still one-size-fits-all. There is no test that can reliably predict patient's response to each treatment. A tremendous amount of time and resource can be wasted before eventually finding an effective treatment for a given patient. The first objective of this project is to validate in a large RA cohort a bioassay that has been developed as a predictor of patient's response to treatments of RA. Blood samples from study subjects that have been recruited to a RA study called TARGET will be subjected to the bioassay and the results will be correlated with their response to treatments. This bioassay once validated will markedly improve clinical care, bringing us one step closer to personalized medicine of RA. The second objective is to study and compare the global gene expression pattern in RA patients before and after effective treatments. Identification of genes, whose expression is altered in active RA but normalized by effective treatments, will bring important insights into the molecular pathways triggering and propagating RA, and eventually lead to early detection, prevention, or even cure of RA.